Optical limiting and nonlinear optical properties of Cr2O3 and WO3 based polymer nanocomposites

Abstract

The optical limiting behavior of templated transition metal nanoparticles Cr2O3 and WO3 in a PMMA host at the wavelength of 1064 nm in the nanosecond regime is discussed. Optical filters were produced by chemical synthesis from the bulk. The optical limiting properties were characterized using an adequate custom-made optical setup and the third order nonlinear parameters, namely the nonlinear absorption coefficients and refractive indices were measured by the Z-scan method. The optical limiting performance improvement is clearly demonstrated for the PMMA/Cr2O3 filter bearing out a laser protection level of OD = 1.2, a factor of 4 larger than the pure PMMA filter. A significant blue shift in the nonlinear activation threshold energy occurs when WO3 or Cr2O3 are embedded in a PMMA host as the values have been subsequently pulled down from 500 µJ (pure PMMA) to 65 µJ and 23µJ, respectively. Z-scan measurements highlighted a self-defocusing effect as a result of a negative nonlinearity. Nonlinear refractive indexes in the order of n2 = −1.0X10−15cm2/Wwere calculated for the PMMA/Cr2O3 and PMMA/ WO3 systems. A nonlinear absorption coefficient as high as β = 163cm/GW was measured for the PMMA/Cr2O3 optical limiting filter while the one for PMMA/ WO3 lies 1 order of magnitude behind. It is suggested that the PMMA/Cr2O3 optical system undergoes reverse saturable absorption enhanced by excited state absorption (ESA/RSA). Besides, it is believed that multi-photons absorption (MPA) occurs in PMMA/WO3 or pure PMMA.